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Hey guys,

Me and my mate are currently welding up the frame on my custom mini which is made from tubular steel. We are having problems getting the TIG welder to produce a good weld in places and I have asked my mate James to explain the issue below:

"Welding problem:

Setup as follows: Tig welding ~3-4mm mild steel @ max of 120A, HF start. Argon shield, 10 to 12 l/min IIRC (though not verified on a flowmeter), 2-3 sec of post-weld flow. Using pedal for up and down slope on current. 1.6mm copper coated, clean fresh filler rod.

*Two problems. The first is the galvanised pipe, after sanding it back to steel (as opposed to zinc) it is still contaminating the weld and there's a white smoke/powder forms around some sections of the weld. Weld tends to contain voids. I guess this is just tiny traces of the zinc left after sanding?

*Clean mild steel. Some welds are fine, exactly as expected, neat fishscales then others on the same material form numerous small voids that wont close up or if they do end up as hidden bubbles in the weld. As you ramp the current down the final bubble often grows as it cools into a sort of hollow boil on the surface of the weld (as opposed to the more normal shallow depression and small pimple).

I can't see any common difference in setup or materials between welds that work and those that are shit. Human error, bad technique (I'm self taught having read a couple of books so I readily accept this is most likely though I have little problem on aluminium)? Bad filler? Bad stock? Wrong flow?"

Sorry for the mahoosive post. We may try welding the frame using a MIG or gas welder, so if this is a better option, I would appreciate any advice at all from experienced welders on here.

Cheers

"If i'm not in action...i'm in traction"

You may have too much gas flow there ny friend. Other than that your getting contamination from some where have you tried warming the metal first?

Own the day

Edited by Rod S on 31st Oct, 2008.

Schrödinger's cat - so which one am I ???

make sure to wear masks when welding galvinized tube as the fumes given off are not good for you

Build Thread Click Here

Thanks for all the advice so far guys very helpful. I have spoken to my mate James and he has this in reply:

"Oxidation from the rear is a very definite possibility and one I hadn't really considered. With the benefit of (iffy) hindsight it is more of a problem where the gap is 'big' or I'm doing pipes where the inside may not be fully clean. I'm not closing pipe/tube, I'm aware that the hot internal air is a problem when doing so.

Tungsten is correct type and 2.4mm, ground to a point (axial grind marks)

Too much gas is a possibility, it's something I need to look into to save money if nothing else but it's not blowing the bubbles in the puddle, they seem to form in the metal then surface."

"If i'm not in action...i'm in traction"

Bring the gas flow down to 8 l/min, should stop the holes forming and give a neater weld

Paul

I seriously doubt it!

are you sure its the right tungsten?

Sorry to bring up old thread but may help others. The higher gas flow as a few others have said will cause big problems with weld quality. When you go too high turbulence occurs and you end up pulling air into what should be, inert atmosphere.

So drop down to 8l a min max I weld at 6lpm but everyone has slightly different methods and also depends on draughts etc. Most of my work is stainless so the 8 may be better

Get yourself a small pieced of titaium. This will show up any problems with your gas and flow. I weld anything from titanium, nickel alloys, aluminium, stainless, colbalt, carbon steels and have my gas set to 14lpm. My equiptment is calibrated every 6 months and is aerospace verified.
I suspect that it's your cleaning of the material is the cause. The galvinised surface is finding it's way into the weld and disrupting the grain pattern of the base material.
I also think that the voids your getting is from the weld not being purged with argon from the back of the weld.

Madcat, I guess 14lpm could work fine but will depend on shroud size. if you have a nice big diameter shroud then no problem. if your using very small diameter shroud (most tig kits supplied with these) then 14 would be too high imo and cause probs.

However it sounds like you are a much more experienced welder than me so would love to hear your views on this :)

Oh yes good point. I use a wide ceramic. A wide ceramic is best all round if gas usage is not a problem. Also tungsten projection (amount the tip of the tungsten stands proud of the ceramic) I'll take a photo of my torch while I'm at work tomorrow and post it on this thread.